>50v Preventing RCD Trip Timing.

[JimG]

Hi Folks,

Would welcome input/advice on the following:

Started working on a house which looks like it's been rewired probably within the last 3 yrs.

TT sytem: New'ish CU (S-Type RCD main Sw + RCD protecting 3 rings - up/dwn & kitchen. Lights, bonding all check-out ok!

Both Up & dwn rings check-out great - both have good R1/Rn & R2 readings. R1+R2 + Ze giving max Zs readings well under 7671 requirements for type 'B' MCB's. Insulation >200 & RCD trips @ 12mS.

Issue is with the kitchen ring! R1/Rn & R2 all look good. R1+R2 appears ok. Insulation >200, BUT upon testing the the RCD, my Diolog tester indicates a >50v present and I cannot acquire a trip time? The RCD trips but as said I cannot record a trip time?

I look fwd to any advice .......

Rgds,

JimG.

 

[sparkyork]

hi mate, if all circuits and kitchen test out ok then could it be something thats plugged in on the kitchen circuit thats somehow causing the problem?

 

[Evans Electric]

Thats weird !! Can't be of much help , where is this 50 volts showing , on your meter ?

The other RCDs are tripping OK so the earth path is OK , the Meter is OK . I have come across quite a lot of faulty RCDs lately !. Can you swop it with one of the others, see if it plays up on another circuit.

Try it without the ring connected, just a temp. plug for the tester.

The words straw and clutching at come to mind .

 

[JimG]

I've checked-out what I could thinking the same thing? I'm back there 2morrow and will run thru it again with a clearer head.

Appreciate yr response.

JimG.

 

[JimG]

Goog point Evans E - I'll give a bash 2morrow.

Rgds,

JimG.

 

[JimG]

...sorry. Yep, the 50v is showing on my meter?

 

[paulh]

either the rcd isn't quick enough(swap out) or the zs is to high ie: over 1660 ohms.

Maybe knowing some of your results might help.

Good luck

 

[paulh]

To test the rcd for the cct you are disconnecting the outgoing cct. You can test with the load connected but gn3 suggests disconnecting the outgoing cct. This also removes other variables (parallel paths etc).

 

[dan.]

test it at the cu with 3 leads instead of the plug top with the mcb switched off

 

[steptoe]

sounds as tho the RCD is not reacting quick enough to earth to prevent a touch of >50v appearing on the CPC.

can you do a ramp test with a dilog?

prob simplest way is to swap out the RCD, or is this the S type one? you will need a tester that is capable of testing S type RCDs, (BTW, prob wont meet 17th for standard domestic if it is S.)

sorry, just re-read the post.

why are you testing your RCD on the ring anyway?

you test the RCD at the board, you are testing the RCD, not the kitchen ring.

I dont understand how you can be getting correct readings but then this one circuit fails to operate the RCD.

 

[dan.]

could try switching off all the other circuits to see if the 50v is an induced voltage?? just a thought.my tester wont let me do some tests if it senses a voltage present either.depends how it was rewired.

 

[kme]

Hi Folks,Would welcome input/advice on the following:

Started working on a house which looks like it's been rewired probably within the last 3 yrs.

TT sytem: New'ish CU (S-Type RCD main Sw + RCD protecting 3 rings - up/dwn & kitchen. Lights, bonding all check-out ok!

Both Up & dwn rings check-out great - both have good R1/Rn & R2 readings. R1+R2 + Ze giving max Zs readings well under 7671 requirements for type 'B' MCB's. Insulation >200 & RCD trips @ 12mS.

Issue is with the kitchen ring! R1/Rn & R2 all look good. R1+R2 appears ok. Insulation >200, BUT upon testing the the RCD, my Diolog tester indicates a >50v present and I cannot acquire a trip time? The RCD trips but as said I cannot record a trip time?

I look fwd to any advice .......

Rgds,

JimG.

What is the actual Ra?

This is nothing to do with an induced voltage. Your meter is not telling you about an actual volage, per se.

What the meter is telling you is that, during the course of the test, the touch voltage with respect to earth, will exceed 50V.

Therefore, it terminated the test.

This is generally caused by a bad or insufficient earth, which is why I want to know what the Ra actually is?

KME

 

[JimG]

KME/Steptoe - appreciate your responses.

The Ra is 47ohms, and I was testing the kitchen ring as you normally do to ensure the RCD is functioning correctly. The RCD actually trips but it's the >50v touch voltage which is concerning me.

I'm in there again today and will run thru it.

Cheers,

JimG.

 

[steptoe]

if the RCD is operating correctly when you test it at the board then it is not at fault,

your kitchen ring is at fault, by not allowing a sufficient current to flow to earth fast enough to prevent the voltage rising above 50v.

IMO you test the RCD at the point of installation, NOwhere else,

I fail to understand how your ring can be giving satisfactory results but failing to maintain good earth integrity to allow the RCD to operate.

are you sure your E continuity does not include parralel paths?

 

[JimG]

Thank you all for your intuitive responses - much appreciated.

So ---- today I discond the ring and chkd the RCD @ the CU - worked a treat --8ms.

Further invetsigated the ring and found - unsighted behind the sink units, an unswitched fused spur! It was in a mess.The damn thing was corroded almost to pieces. I then discovered it was feeding an old water softener unit under the stairs where the mains water-pipe is located. I removed the spur, cleaned-up the cables and simply choc-blocked them together for testing. All is now working ok. Refitted a new spur but leaving this water softener off all circuits. 4hrs of my life wasted sorting-out this crap, but thx guys.

Until the next one ........

Rgds,

JimG.

 

[PAUL M]

Thank you all for your intuitive responses - much appreciated.So ---- today I discond the ring and chkd the RCD @ the CU - worked a treat --8ms.

Further invetsigated the ring and found - unsighted behind the sink units, an unswitched fused spur! It was in a mess.The damn thing was corroded almost to pieces. I then discovered it was feeding an old water softener unit under the stairs where the mains water-pipe is located. I removed the spur, cleaned-up the cables and simply choc-blocked them together for testing. All is now working ok. Refitted a new spur but leaving this water softener off all circuits. 4hrs of my life wasted sorting-out this crap, but thx guys.

Until the next one ........

Rgds,

JimG.

Stick it on the bill mate:^OGuiness Drink]

 

[JimG]

Yoooo bet baby, and then some.

 

[Evans Electric]

Glad you got to the bottom of it, we all live and learn.

 

[paulh]

I don't want to offend.....but.

to quote yourself...Issue is with the kitchen ring! R1/Rn & R2 all look good. R1+R2 appears ok. un quote.

Looks like we all wasted our brain pills as a ring final continuity test would of showed up a spur and probably the fault.

A lesson learnt for next time. :|

 

[steptoe]

at least you found it in the end.

one more marked off the list,

ding,